Effect of Ag Addition to Au Catalysts for the Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The addition of Ag to Au nanocatalysts is known to improve several catalytic reduction and oxidation reactions. Until now, bimetallic AuAg catalysts have not been studied in detail in liquid phase oxidation reactions. We investigated the activity, selectivity, and stability of silica supported Au, Ag and AuAg catalysts in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), an important reaction to produce bio-based polymers. We demonstrate that addition of an optimum amount of inactive Ag to the active Au catalyst substantially increases the overall selectivity and yield of the desired FDCA. Interestingly, Ag addition decreased the conversion rate of the reactant HMF to the intermediate HMFCA, but improved (up to 10–20 % Ag addition) much the conversion of the intermediate product to the desired final product. This is probably due to tuning the electronic properties of the nanoparticles to achieve an optimum adsorption strength of the intermediate on the surface of AuAg catalysts. Moreover, particle growth was suppressed by the bimetallic AuAg catalyst, ultimately leading to superior stability compared to its monometallic counterparts.